grep -c '[^[:space:]]' medals.txt
grep -E "中国|中国香港|中国台北" medals.txt | sort -t"," -k5,5nr
sort -t"," -k4,4nr medals.txt | head -n 5 | cut -d"," -f1
sort -t',' -k2,2nr medals.txt | head -n 5 | awk -F',' '{sum += $2} END {print "金牌总数:", sum}'
